Sick Ants Help Vaccinate Colonies, Study Suggests

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Like crowded megacities, busy ant colonies face a high risk of
disease outbreaks. New research indicates such "urban ants" also
know how to prevent epidemics — when an infected ant enters the
colony, its nest mates carefully lick off the infecting fungus.

"This is increasing the survival of the originally exposed
individual," study researcher Sylvia Cremer, of the Institute of
Science and Technology Austria, told LiveScience.

And it turns out, the licking behavior may also help the doer by
giving that individual
greater immunity to the infecting fungus. Insects don't have
the "adaptive" immune system that mammals do, but they are still
able to fine-tune their disease-fighting systems to react to
specific threats.

Fluorescent fungus

In nature, ants would pick up a fungal or other infection likely
during foraging when they scamper across a cadaver of an infected
ant or grasshopper, for instance, Cremer said.

To figure out how Lasius neglectus ants would react to
such a diseased nest mate, the researchers infected one
individual ant with fluorescent-labeled spores
of fungus and let them interact with other members of their
colony, tracking where the fluorescent spores ended up.

The researchers found that when this infected ant returned to the
colony, its nest mates don't avoid it. Instead of running from
the infected and contagious insect, the ants approached their
colony mate and licked it, seemingto remove pathogens from the
sick ant's body, a
social grooming behavior.

The originally infected ant had less of a chance of dying once
its nest mates remove the spores, the researchers saw. This
licking behavior exposes the healthy ants to a very small amount
of the fungus, which was enough to be detected by tests the
scientists ran. However, the small amount of fungus didn't make
those licking ants sick.

The researchers saw that during this low-level infection, a set
of immune genes related to anti-fungal defenses was activated in
the ants. Lab tests then revealed that when later exposed to this
fungus, these ants were better able to fight it off.

Herd immunity

The researchers made a computer model using data from their
experiments and discovered that this licking behavior, while it
kills a low number of ants, would enable a colony as a whole to
recover from a fungal infection more quickly.

The licking behavior is similar to the human concept of a
vaccine, which exposes people to a weakened or dead strain of
virus to prime their immune system. Humans didn't discover
protective immunity until Edward Jenner created the smallpox
vaccine in 1796.

These types of interventions work best when the whole population
is treated, giving rise to "herd immunity," in which even
nonimmunized individuals aren't at risk of the disease because
they are surrounded by immune individuals.

The study was published today (April 3) in the journal PLoS
Biology.

You can follow LiveScience staff writer Jennifer Welsh on
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